Genetic influences on the increase in blood pressure with age in normotensive subjects in Barbados.

The authors tested the single and combined effects of nuclear and mitochondrial DNA genotypes on the phenotypes of systolic blood pressure (SBP) and weight, and their changes over 5 years in normotensive subjects living in Barbados. The nuclear genotypes were gender (Y chromosome), haptoglobin (HP), and group specific component (Gc). A mitochondrial genotype was chosen as a marker for maternal lineage. Baseline clinic SBP and weight (N=78), 24-hour SBP (N=28) were measured. Five years later, clinic SBP and weight were measured again in 28 participants. Male participants generally had higher pressures than female participants. The HP genotype was associated with 5 of the 8 SBP phenotypes. The haptoglobin-1 (HP1) allele was associated with higher clinic (P=.024) and evening SBP at baseline (P=.020). The effect of HP1 appears to be dominant. Haptoglobin-2 (HP2) was associated with the increase in weight over 5 years (P=.002). Group specific component (Gc) genotype was associated with 6 of the 8 SBP phenotypes. The Gc polymorphism 2 was associated with higher 24-hour SBP, sleep SBP (midnight-6 AM), afternoon SBP (noon-6 PM) and evening SBP (6 PM to midnight). Furthermore, we found a significant association between the haptoglobin/mt-DNA and Gc/mt-DNA polymorphisms with SBP between 6 PM and midnight (P=.009 and P=.011, respectively). The 5-year changes in SBP were significantly associated with the haptoglobin/mt-DNA and Gc/mt-DNA polymorphisms (P=.005 and P=.011, respectively). Multivariate analysis for genetic effects on change in weight and change in BP suggested the rise in BP, but was not suggestive of change in weight. Furthermore, multivariate analysis was associated with Gc, but not Haptoglobin genotype. In normotensive subjects of African descent living in Barbados, the increase in blood pressure with age is significantly influenced by both nuclear and mitochondrial genotypes that are more common in African derived populations.

Blood pressure variation in blacks: genetic factors

Persons of African descent living in the Western hemisphere, including African Americans, have the highest prevalence of hypertension in the world. Debates continue as to whether it is their African ancestry or the western environment that is more important in increasing the prevalence of hypertension in the African Diaspora above that of indigenous Africans as well as of fellow inhabitants in the Western Hemisphere. Current data support that hypertension in African Americans, like that in other population groups, arises from the interaction of environmental factors with a susceptible physiology that is determined in part by genetic factors. Dietary sodium chloride (NaCl) is an important environmental factor, and the inability to prevent blood pressure from increasing to hypertentive levels in response to the comparitively high NaCl content of Western diets characterises the majority of hypertensive African Americans. Studies discussed herein suggest a strong genetic component for the physiology of salt "salt sensitivity". Phenotypes that are indicative of this sensitivity are more common in African Americans than in Americans of European descent and in hypertensive African Americans compared with normotensive African Americans. Further studies are needed to more clearly define these genetic markers that determine salt sensitivity. (AU)

Blood pressure in blacks: twin studies in Barbados

We have recently reported that there are significant genetic influences on the population variation in blood pressure in black twins in Los Angeles. The present cross-sectional study was undertaken to replicate these findings in a black twin population that lives in a different biosocial environment. We chose the Caribbean island nation of Barbados, where 96 percent of the population is black, the literacy rate is 99 percent, and the access to health care is guaranteed. The goals were 1) to test the feasibility of twin studies in blood pressure research in a developing country and 2) to estimate the relative contribution of genes and environment to blood pressure variability in blacks in the Caribbean. The names of 200 twin sets were obtained with the assistance of community resources including a twin club, by media advertisement, and by asking people at public blood pressure screenings if they knew any twins. By using these methods, we identified 200 sets of twins. Of these, 37.5 percent (75/200) met our criteria for study. Although 97 percent of the sets of twins (73/75) said they were willing to participate, only 69 percent (52/75) were able to be scheduled during the 1 week of the study when the full team of investigators was in Barbados. Of those scheduled, 83 percent (43/52) were examined. Examination included medical history, physical examination, recumbent blood pressure measurements by two observers, anthropometric measurements, 24-hour urine collections for sodium and potassium tests, and blood tests for zygosity. (ABSTRACT TRUNCATED AT 250 WORDS) (AU)

Slavery, salt and survival: a hypothesis on the greater prevalence of high blood pressure in Western Hemisphere blacks

High blood pressure of unknown cause (essential hypertension) is the major chronic illness contributing to premature morbidity and mortality in western hemisphere Blacks. As a group, blacks in the western hemisphere have higher mean blood pressure levels than blacks from Sub-Sahara Africa where essential hypertension is strickingly less common. Because of the similar heritage of these populations it has been suggested that blood pressure differences between them is most likely due to environmental differences such as variations in diet or biobehavioral stress. We suggest a new hypothesis: selective survival related to sodium (Na+) metabolism during the slavery period of Western hemisphere blacks and Sub-Sahara African Blacks which now play a major role in these geographic variations in blood pressure. Most blacks in the western hemisphere are descendants from a population of sub-Saharan Africans that survived the selection pressure of the trans-Atlantic slave trade and new world slavery; ancestors of most current Black Africans had no such experience. The present atricle reviews the importance of Na+ metabolism in the causes of mortality during the slave trade and estimates Na+ losses due to sweating, diarrhea and vomiting. The magnitude of these potential losses make it likely that fatal Na+ depletion was a major contributor to the high mortality. Thus, we suggest that the slave trade imposed severe demands on Na+ homepstasis and those most likely to survive were most capable of conserving Na+ than those who did not. In today's high dietary Na+ enviroment the descendants of African slaves may be more susceptible to Na+ sensitive" hypertension than the descendents of Black Africans without this heritage. (AU)

Slavery, salt, and survival: a hypothesis of the greater prevalence of high blood pressure in Western Hemisphere blacks

High blood pressure of unknown cause (essential hypertension) is the major chronic illness contributing to premature morbidity and mortality in Western Hemisphere Blacks. As a group, Blacks in the Western hemisphere have higher mean blood pressure levels than Blacks from Sub-Sahara Africa where essential hypertension is strikingly less common. Because of the similiar heritage of these populations it has been suggested that blood pressure differences between them is most likely due to environmental differences between them is most likely due to environmental differences such as variations in diet or behavioral stress. We suggest a new hypothesis: selective survival related to sodium (Na+) metabolism during the slavery period of Western hemisphere history has led to inherited genetic differences between Western hemisphere Blacks and Sub-Sahara African Blacks which now play a major role in these geographic variations in blood pressure. Most Blacks in the Western hemisphere are descendants from a population of sub-Saharan Africans that survived the select pressure of the trans-Atlantic slave trade and New World slavery; ancestors of most current Black Africans had no such experience. The present article reviews the importance of Na+ metabolism in the causes of mortality during the slave trade and estimates Na+ losses due to sweating, diarrhea and vomitting. The magnitude of these potential losses make it likely that fatal Na+ depletion was a major contributor to the high mortality. Thus, we suggest that slave trade imposed severe demands on Na+ homeostasis and those most likely to survive were more capable of conserving Na+ than those who did not. In today's high dietary Na+ environment the descendents of African slaves may be more susceptible to "Na+ sensitive" hypertension than the descendents of Black Africans without this heritage

Slavery, salt, and survival: a hypothesis of the greater prevalence of high blood pressure in Western Hemisphere blacks

High blood pressure of unknown cause (essential hypertension) is the major chronic illness contributing to premature morbidity and mortality in Western Hemisphere Blacks. As a group, Blacks in the Western hemisphere have higher mean blood pressure levels than Blacks from Sub-Sahara Africa where essential hypertension is strikingly less common. Because of the similiar heritage of these populations it has been suggested that blood pressure differences between them is most likely due to environmental differences between them is most likely due to environmental differences such as variations in diet or behavioral stress. We suggest a new hypothesis: selective survival related to sodium (Na+) metabolism during the slavery period of Western hemisphere history has led to inherited genetic differences between Western hemisphere Blacks and Sub-Sahara African Blacks which now play a major role in these geographic variations in blood pressure. Most Blacks in the Western hemisphere are descendants from a population of sub-Saharan Africans that survived the select pressure of the trans-Atlantic slave trade and New World slavery; ancestors of most current Black Africans had no such experience. The present article reviews the importance of Na+ metabolism in the causes of mortality during the slave trade and estimates Na+ losses due to sweating, diarrhea and vomitting. The magnitude of these potential losses make it likely that fatal Na+ depletion was a major contributor to the high mortality. Thus, we suggest that slave trade imposed severe demands on Na+ homeostasis and those most likely to survive were more capable of conserving Na+ than those who did not. In today's high dietary Na+ environment the descendents of African slaves may be more susceptible to "Na+ sensitive" hypertension than the descendents of Black Africans without this heritage (AU)